Hydraulic fracturing is a well-stimulation technique in which subterranean rock is fractured by a hydraulically pressurized fracturing fluid typically made by combining water, an hydraulic fracturing proppant (conventionally sand or aluminum oxide), and additive chemicals that modify subterranean flow, subterranean interfacial tension, and/or provide other effects. A hydraulic fracture is formed by pumping the fracturing fluid into a wellbore at a rate sufficient to increase pressure at the target depth to exceed that of the fracture gradient (pressure gradient) of the rock. When the hydraulic pressure is removed from the well, the hydraulic fracturing proppants lodge within the cracks to hold the fractures open. Hydrocarbon compounds such as natural gas and petroleum are recovered via the cracks in the hydrocarbon-containing deep-rock formations. Hydraulic fracturing techniques can be used to form a new well and can also be used to extend the life of an existing conventional oil well.
Chemical additives including surfactants have been added to fracturing fluids in hydraulic fracturing processes to increase recovery of hydrocarbon compounds from subterranean hydrocarbon-containing formations. The surfactants can act to lower the interfacial tension between the fracturing fluid and the oil trapped within the fractures in the reservoir and can change the wettability of the reservoir rock, thereby increasing the yield of hydrocarbon compounds released from the rock fractures. However, many conventional surfactants and surfactant blends adsorb substantially onto the rock surfaces, depleting the surfactant quickly at the expense of deeper-lying fracture surfaces. Additionally, many injected surfactants facilitate underground emulsion formation between the hydrocarbon compounds and the fracturing fluid, which retards or prevents recovery of the hydrocarbon compounds.
Further, conventional chemical surfactants and mixtures thereof are often unstable or insoluble in the high temperature and/or high total dissolved solids water sources encountered in some subterranean reservoirs. For example, in some reservoirs temperatures in excess of 60° C. are encountered; temperatures can be as high as 250° C. Additionally, underground water is often characterized as having high total dissolved solids, such as about 4 wt % total dissolved solids and as much as about 35 wt % total dissolved solids. In some cases, a substantial portion of the dissolved solids are ionic (one or more salts).
Thus, there is a need in the industry for compositions that reduce the interfacial tension between a fracturing fluid and the oil trapped within the fractured subterranean rock formations without adsorbing strongly to the rock surfaces. There is a need in the industry for compositions that reduce the interfacial tension between a fracturing fluid and the oil trapped within the fractured subterranean rock formations in high temperature environments. There is a need in the industry for compositions that reduce the interfacial tension between a fracturing fluid and the oil trapped within fractured rock formations in subterranean environments having water sources that include high total dissolved solids. There is a need in the industry for compositions that increase the yield of hydrocarbon compounds recovered from fractured subterranean rock formations.